Security systems are generally known. Such systems are typically used to protect a physical space (e.g., a building, a complex of buildings and surrounding spaces, etc.) from intruders.
Intrusion into the protected spaces is often prevented through the use of some form of physical barrier (e.g., walls, fences, etc.) with one or more access points (e.g., doors, windows, etc.). Sensors may be located proximate these access points to detect intruders.
For example, in the case of a door, a perimeter sensor, such as a switch, may be used to detect the opening of such doors. The switch, in turn, may be coupled to an alarm panel through which the security system may be armed and disarmed.
While simple switches may be effective in the case of a building having few doors and windows, they are not cost or labor efficient when securing a multitude of windows or doors. Secondly, switches should not be used as the only line of defense as they can be covertly disabled at the perimeter. In such cases, a motion sensor is needed that covers the broad secured area.
The current practice of motion sensors typically employ Passive Infrared (PIR) technology which detect human body (and unwanted animal) heat against a background and Doppler Microwave (DW) technology which detect changes of returned radio waves as they bounce off a moving object(s).
Known deficiencies of PIR and DW motion sensors include: poor ability to discriminate between small animals (pets or pests) and human intruders; covert thermal cloaking or masking; false alarm triggers upon cycling heating and air conditioning (HVAC) equipment; false alarm triggers upon radio frequency interference (cordless phones, microwave ovens, wireless networking) and false triggering upon large body disturbances (cars) behind exterior walls.
Intrusion motion detectors based upon the processing of video images could be used in such cases, but they are also subject to a number of challenges. In this regard, discriminating small animals (pets or pests) from humans; objects that sway in the wind (e.g., tree branches in a window, curtains); moving shadows, lights or abrupt changes in room lighting conditions can cause false alarms. With the above limitations in current practices noted, more reliable methods for detecting human intrusion threats are needed.